Determining Clock Accuracy Requirements for UART Communications

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Determining Clock Accuracy Requirements for UART Communications

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This application note discusses the timing requirements for the commonly used serial asynchronous
communications protocol implemented in UARTs, and shows how to determine the tolerance for the UART clock
source at both ends of an asynchronous link.

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Background
The RS-232 specification dates back to 1962, when it was first released by the EIA (Electronic Industries
Association). The specification has changed over time, incorporating higher data rates and closing the
compatibility gaps between TIA (Telecommunication Industry Association) and international (ITU, ISO)
standards. The current version of the RS-232 specification is EIA/TIA-232-F, dated October 1997.
The protocol benefited from the availability of MSI ICs from the late 1970s which had the complexity to handle
the standard at reasonable cost. These ICs are generically called UARTs (Universal Asynchronous Receive
Transmit). Many LSI ICs (including microcontrollers) now include the functionality.
As is often the case, the availability of UARTs drove the industry to use the RS-232 serial protocol in non-RS-232
ways. Common examples are RS-485 transmissions, opto-isolated transmissions, and transmissions using a
single-ended physical layer (i.e. 0 - 3.3V instead of ±5V or ±10V). This note covers the general timing aspects
of the serial interface, not application nuances of handshaking or the physical layer, and so is applicable to all
generalized UART applications.

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maxim

huacc121

Thanks a lot~~ 感謝分享~

NMDNBA

Thanks a lot